Method of making a valve lifiter



June 14, 1966 G. H. ROBINSON ETAL 3,255,513

METHOD OF MAKING A VALVE LIFTER Original Filed Aug. 17, 1962 INVENTORS BY [award $012025! A ORNEY United States Patent 3,255,513 7 METHOD OF MAKING A VALVE LIFTER George H. Robinson, Rochester, and Edward R. Mantel,

Warren, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Original application Aug. 17, 1962, Ser. No. 217,700, now

Patent No. 3,198,182, dated June 22, 1965. Divided and this application Feb. 13, 1964, Ser. No. 344,630

4 Claims. (Cl. 29-156.7)

This .is a division of the'United States patent applias Patent No. 3,198,182, dated June 22, 1965, and assigned to the assignee of the present invention.

This invention relates to valve lifters for transmitting movement from a camor the like to the stem of a poppet valve such as is used in internal combustion engines and more particularly to an improved valve lifter and a method for manufacturing the valve lifter.

The general design of valve lifters in common use today comprises a generally cup-shaped cylinder which is slidably reciprocable in a bore provided therefor in the engine crank case so as to contact the engine driven cam and 'a separately formed member which is thrustably supported in the lifter cylinder and serves to transmit movement from the lifter to the push rod.

It is particularly important in valve lifter construction that the valve lifter working surface or foot as it is called in the art, operating against the cam, be formed of awear-resistant material since these contacting parts are subject to severe wear conditions in service. It is the object of this invention to provide an improved valve litter and a method for its manufacture. It is a more specific object of this invention to provide a valve lifter having a more wear-resistant foot portion.

These and other objects are accomplished by preparing an intimate mixture of powdered carbon, tungsten, molybdenum, silicon and iron in certain proportions and compressing them to form a thin briquette or wafer in a manner well known in powdered metallurgy art. The valve lifter working end is preferably provided with a peripheral retaining ridge or lip whereby a shallow cavity is formed within the ridge. The briquette is then placed within the cavity and the briquette and adjacent valve lifter surface are subjected to heat at a temperature in the vicinity of 2200 F. for a time sufficient to cause the constituents of the briquette to fuse together and effect a diffusion bond with the steel face. On completion of the fusion cycle the interior of the steel body is cooled rapidly to promote directional solidification of the coating alloy from the valve lifter surface alloy interface outward, thus preventing formation of internal shrinkage cavities in the coating.

Other objects and advantages of the invention willbe apparent from the following detailed description made in relation to the accompanying drawing, in which:

FIGURE 1 is a fragmentary elevation view of a valve tappet in its engine environment;

FIGURE 2 is a crosssectional view of a valve tappet body; and

FIGURES 3, 4 and 5 are fragmentary cross-sectional views illustrating sequential steps in the process of this invention.

As shown in FIGURE 1 of the drawings, a valve lifter the lifter body and the push rod during engine opcation Serial No. 217,700, filed August 17,1962, issued Patented June 14, 1966 eration. Overlying the seat member 20 and the shoulder 21 there is provided a thin metal retaining washer 23. The washer is relatively flexible and of somewhat greater diameter than the opening 15 so that on being radially deflected and forced against this opening, as shown, it will contract sufficiently to enable it to enter the opening. It may readily be seen that an upward movement of the rod 18 causes the washer to lock or wedge against the opening 15 and to lock the seat 20 within the valve lifter.

This invention is concerned with a method of making a litter body 10 and in particular a method of providing the closed end 12 with an end face .24 or foot of a wear-resistant material. In general the method involves first forming a cup-like member consisting of a cylinder which is closed on one end such as is shown in FIGURE 2 by a simple upsetting or cold extrusion operation. The dies employed in this operation also provide the closed end of the valve lifter with the peripheral ridge 26 of about 0.015 inch in height which terminates in a relatively narrow edge 28 and has an inwardly slanting side 30. This side 30 may suitably slant at an angle of about 45. The height of the ridge 26 may suitably vary from about 0.010 inch to about 0.030 inch. As will be hereinafter explained in detail, the process of this invention involves the application of a wear-resistant alloy within the cavity defined by the ridge 26.

After the upsetting operation the surfaces of the lifter between the ridge 26 are preferably grit blasted to clean them. A powdered metal mixture is next prepared which preferably consists of, by weight, 2.6% carbon, 4% molybdenum, 4% tungsten, 2.0% silicon and the balance iron. These materials are present in the form of powders preferably having a particle size which will pass a mesh screen. The powders are thoroughly mixed and then compressed under a pressure of about 30 tons per square inch into a briquette 32, FIGURE 3, preferably having a thickness of about 0.15 inch.

Suitable valve lifter working surfaces may be made in accordance with this invention by providing a briquette in which the carbon is present between about 2.0% and 3.5% by weight, the molybdenum at least 2.0% by After the briquette has been formed, it is preferably sintered to obtain increased strength for handling efficiency and then placed within the confines of the cavity of the retaining lip 26. The briquette is preferably sufficiently smaller in diameter than the valve lifter so that it rests flatly on the lifter surface within the ridge 26 as shown in FIGURE 4. Preferably a flux such as borax is next sprinkled over the briquette. The briquette and adjacent valve lifter surface are then subjected to heat within a temperature range of about 2200 F. to 2400 F. by means of an induction coil 22 as shown in FIGURE 4 in a manner such that the heating effect is concentrated within the briquette and at the interface of the lifter surface and the briquette. Heating temperatures in excess of 2400 F. may be used. However, no advantage is obtained at higher temperatures. Higher heating temperatures tend to cause excessive erosion of the retaining ridge 26 and for this reason are undesirable. The heating operation causes the powdered metal to fuse to form a coating alloy 24. In this heating operation the flux promotes the formation of a fluid slag and thereby a smooth uniform surface. The fused coatingcomposition accordingly differs from the briquette composition in that the carbon content ranges from about 1.5% to 3.0% by weight and the silicon ranges from about 0.5% to about 3.0%. The molybdenum and tungsten content of the fused coating is at least 2% each and not greater than 10%. In general, the briquette composition previously described will, inaccordance with the process of this invention, result in the fused coating composition above described. In the specific embodiment described herein, thefused coating has a composition of about 2.1% carbon, 1.5% silicon, 4.0% tungsten, 4.0% molybdenum, and the balance iron. It will be noted that the composition of the fused coating involves a loss of about 0.5% by weight each of carbon and silicon. During the fusion cycle, the carbon diffuses into the iron particles which in their originalform are of a relatively pure low carbon composition. This reduces the melting point of the iron to a temperature in the vicinity of 2200 F. At this temperature, denum dissolve into the molten ferrous metal. The molten alloy flows across the valve lifter surface so as to form a relatively smooth coating extending between the extremities of the ridge 26. During the heating step, the alloy, and particularly the carbon thereof, diffuses into the steel body to form a strong diffusion bond. It will, of course, be understood that it is the diffusion coating ranges which are essential to the high quality performance of the valve lifter of this invention. The briquette composition may be varied to take into account process variables which-may result in a greater or lesser loss of carbon and silicon.

Oncompletion of the fusion cycle the interior of the steel body is cooled rapidly, preferably by means of a small water jet 34 inserted within the valve lifter body as shown in FIGURE 5 to promote directional solidification of the coating alloy from the alloy-steel interface outward, thus preventing formation of internal shrinkage cavities in the coating. Preferably the heating operation is conducted in a protective atmosphere of nitrogen or suitable endothermic generated gas to prevent excessive oxidation of the metals during heating. After cooling, the coating is ground to a thickness preferably in the range of about 0.01 inch to 0.03 inch and other portions of the valve lifter are ground to size. 1 Finally, the entire valve lifter is carburized to provide the side walls thereof with a wear-resistant surface. This involves heating the lifter in a suitable carburization atmosphere to a temperature in the range of about 1550" F. to 1650 F. As a consequence of this heating operation a carbon case is developed along the sides of the lifter body. During the subsequent quenching the coating 24 is also hardened. The simultaneous carburization of the lifter body and hardening of the coating in a single operation constitutes an important advantage of this invention.

The method of this invention has a number of important advantages. In addition to its excellent wear resistance,

the use of an iron base alloy briquette or coating promotes the formation of a strong diffusion bond between the coating and the steel body. In addition the relatively high carbon content of the alloy results in carburization of the underlying steel during the fusing process and thus provides a layer 36 of harder steel for supporting the coating under high contact loads. The carburized layer 36 in the preferred embodiment is about 0.015 inch. Typically, this carburized layer is about 0.010 inch to 0.020 inch in thickness. The method of this invention may be employed to apply wear-resistant coatings of any thickness and especially thin coatings with a negligible wasteof coating materials. The presence of the retaining lip 26 is essential in that it serves as a dam while the coating alloy is yet molten and thereby insures that the coating layer will be of a satisfactory thickness which will extend uniformly over the entire area of the valve lifter working surface. Although induction heating is prs fsfl'rcd'because the heating is therethe tungsten and molyb- In the preferred embodiment of the invention as described above the valve lifter body 10 is formed from an extrudible low carbon steel such as, for example, SAE 1018 steel containing about 0.15% to 0.20% carbon, 0.6% to 0.9% manganese, a maximum of 0.04% phosphorous and a maximum of 0.05% sulfur. In some instances, it may be desired to make the valve lifter of a stainless steel to provide it with resistance to corrosion. It has been found that typical hardenable stainless steels such as those containing 0.95% to 1.2% carbon and 16% to 18% chromium tend to harden during the application of the foot coating as described above. This results in a cracking of the coating due to volume increase or transformation stresses produced in the hardening operation. Howevenstainless steel valve lifters may be provided in accordance with this invention by using a nonhardenable stainless steel such as the SAE 430 stainless steel containing about 0.12% carbon maximum and 14% to 18% chromium. The wear-resistant coating is applied to the foot as described above. The lifter is then ground to size and carburized as in the case of the low carbonsteel.

While this invention has been described with reference to certain preferred embodiments and conditions, it will be understood that the invention is not limited thereby and that changes and modifications will be apparent to those skilled in the art without departing from the spirit and principles of the invention.

We claim:

1. A method of making a valve lifter having a wearresistant foot coating comprising the steps of forming a tubular low carbon steel element closed on one end thereof to form a foot, said foot having a peripheral ridge thereon defining a recess, forming a powdered metal briquette adapted to be supported within said recess, said briquette being composed of a powdered metal mixture consisting essentially of by weight about 2.0% to 3.5% carbon, at least 2% molybdenum, at least 2% tungsten, the sum of the molybdenum and tungsten being not greater than 12%, about 1% to 3.5% silicon and the balance substantially iron, placing said briquette in said recess, subjecting the briquette to heat at a temperature and for a time sufiicient to cause the briquette to fuse and flow across said recess and for the carbon of said briquette to diffuse into the low carbon steel body to form a diffusion bond, said diffusion forming a hard carburized layer beneath said coating for supporting said coating, and playing a .cooling fluid on the underside of said foot at a rate sufficient to promote directional solidification of the coating from the steel surface outward thereby preventing internal shrinkage cavities therein. a Y I 2. The method of claim 1 in which additionally said valve lifter is heated in a carburization atmosphere to a temperature in the range of about 1550 F. to 1650" F. and quenched whereby said coating is hardened and a carbon case is developed on the surfaces of the valve lifter.

3.A method of making a valve lifter having a wearresistant foot coating comprising the steps of forming a consisting essentially of by weight about 2.0% to 3.5%

carbon, at least 2% molybdenum, at least 2% tungsten,

the sum of the molybdenum and tungsten being not greater than 12%, about 1% to 3.5% silicon and the balance substantially iron, subjecting the briquette to heat at a temperature and for a time sufiicient to cause the briquette to melt and flow across said recess within said ridge and for constituents of said briquette to diffuse into the ferrous element to form a diffusion bond, said diffusion process including a diifusion of carbon into the base metal to -form a hard carburized layer supporting said coating, and cooling the under side of said foot at a rate suflicient to promote directional solidification from the foot surface outwardly thereby preventing internalshrinking cavities in said coating.

4. A method of making a valve lifter having awearresistant foot coating comprising the steps of forming a tubular low carbon steel element closed on one end thereof to form a foot, said foot having a peripheral ridge thereon forming a recess, forming a powderedmetal briquette adapted to be supported in said recess, said briquette being composed of a powdered metal mixture consisting essentially of by weight about 2.0% to 3.5% carbon, at least 2% molybdenum, at least 2% tungsten, the sum of the molybdenum and tungsten being not greater than 12%, about 1% to 3.5% silicon and the balance substantially iron, placing said briquette in said recess, subjecting the briquette to heat at a temperature for a time suflicient to cause the briquette to fuse and flow across said recess and for the carbon .of said briquette to diffuse into the low carbon steel body to form a diifused bond, said diflfusion process forming a hard carburized layer beneath said coating for supporting said coating, said heating being continued to 'cause said coating to have a composition by weight of about 1.5% to 3.0% carbon, at least 2% molybdenum and at least 2% tungsten, the combined molybdenum and tungsten being not more than about 10%, about 0.5% i

to 3.0% silicon and the balance substantially iron and cooling the under side of said foot at a rate sufiicient to permit directional solidification of the coating from the foot surfaceoutward thereby preventing internal shrinkage cavities in said coating.

References Cited by the Examiner UNITED STATES PATENTS 1,606,181 11/1926 Rich. 1,745,886 2/ 1930 Bissell et al.

2,562,543 7/1951 Gippert -l23 2,823,992 2/ 1958 Bolkcom et al. 75-123 3,124,869 3/ 1964 Behnke et al. 29-156.7

FOREIGN PATENTS 801,042 9/ 1958 Great Britain.

JOHN F. CAMPBELL, Primary Examiner.

WHITMORE A. WILTZ, Examiner. I. C. HOLMAN, P. M. COHEN, Assistant Examiners. 

1. A METHOD OF MAKING A VALVE LIFTER HAVING A WEARRESISTANT FOOT COATING COMPRISING THE STEPS OF FORMING A TUBULAR LOW CARBON STEEL ELEMENT CLOSED ON ONE END THEREOF TO FORM A FOOT, SAID FOOT HAVING A PERIPHERAL RIDGE THEREON DEFINING A RECESS, FORMING A POWDERED METAL BRIQUETTE ADAPTED TO BE SUPPORTED WITHIN SAID RECESS, SAID BRIQUETTE BEING COMPOSED OF A POWDERED METAL MIXTURE CONSISTING ESSENTIALLY OF BY WEIGHT ABOUT 2.0% TO 3.5% CARBON, AT LEAST 2% MOLYBDENUM, AT LEAST 2% TUNGSTEN, THE SUM OF THE MOLYBDENUM AND TUNGSTEN BEING NOT GREATER THAN 12%, ABOUT 1% TO 3.0% SILICON AND THE BALANCE SUBSTANTIALLY IRON, PLACING SAID BRIQUETTE IN SAID RECESS, SUBJECTING THE BRIQUETTE TO HEAT AT A TEMPERATURE AND FOR A TIME SUFFICIENT TO CAUSE THE BRIQUETTE TO FUSE AND FLOW ACROSS SAID RECESS AND FOR THE CARBON OF SAID BRIQUETTE TO DIFFUSE INTO THE LOW CARBON STEEL BODY TO FORM A DIFFUSION BOND, SAID DIFFUSION FORMING A HARD CARBURIZED LAYER BENEATH SAID COATING FOR SUPPORTING SAID COATING, AND PLAYING A COOLING FLUID ON THE UNDERSIDE OF SAID FOOT AT A RATE SUFFICIENT TO PROMOTE DIRECTIONAL SOLIDIFICATION OF THE COATING FROM THE STEEL SURFACE OUTWARD THEREBY PREVENTING INTERNAL SHRINKAGE CAVITIES THEREIN.
 4. A METHOD OF MAKING A VALVE LIFTER HAVING A WEARRESISTANT FOOT COATING COMPRISING THE STEPS OF FORMING A TUBULAR LOW CARBON STEEL ELEMENT CLOSED ON ONE END THEREOF TO FORM A FOOT, SAID FOOT HAVING A PERIPHERAL RIDGE THEREON FORMING A RECESS, FORMING A POWDERED METAL BRIQUETTE ADAPTED TO BE SUPPORTED IN SAID RECESS, SAID BRIQUETTE BEING COMPOSED OF A POWDERED METAL MIXTURE CONSISTING ESSENTIALLY OF BY WEIGHT ABOUT 2.0% TO 3.5% CARBON, AT LEAST 2% MOLYBDENUM, AT LEAST 2% TUNGSTEN, THE SUM OF THE MOLYBDENUM AND TUNGSTEN BEING NOT GREATER THAN 12%, ABOUT 1% TO 3.5% SILICON AND THE BALANCE SUBSTANTIALLY IRON, PLACING SAID BRIQUETTE IN SAID RECESS, SUBJECTING THE BRIQUETTE TO HEAT AT A TEMPERATURE FOR A TIME SUFFICIENT TO CAUSE THE BRIQUETTE TO FUSE AND FLOW ACROSS SAID RECESS AND FOR THE CARBON OF SAID BRIQUETTE TO DIFFUSE INTO THE LOW CARBON STEEL BODY TO FORM A DIFFUSED BOND, SAID DIFFUSION PROCESS FORMING A HARD CARBURIZED LAYER BENEATH SAID COATING FOR SUPPORTING SAID COATING, SAID HEATING BEING CONTINUED TO CAUSE SAID COATING TO HAVE A COMPOSITION BY WEIGHT OF ABOUT 1.5% TO 3.0% CARBON, AT LEAST 2% MOLYBDENUM AND AT LEAST 2% TUNGSTEN, THE COMBINED MOLYBDENUM AND TUNSTEN BEING NOT MORE THAN ABOUT 10%, ABOUT 0.5% TO 3/9% SILICON AND THE BALANCE SUBSTANTIALLY IRON AND COOLING THE UNDER SIDE OF SAID FOOT AT A RATE SUFFICIENT TO PERMIT DIRECTIONAL SOLIDIFICATION OF THE COATING FROM THE FOOT SURFACE OUTWARD THEREBY PREVENTING INTERNAL SHRINKAGE CAVITIES IN SAID COATING. 